Having good mechanical properties, heat resistance, chemical resistance and moldability in good balance, polyamide resins are widely used, for example, for parts of electric and electronic appliances and for automobile parts. The recent requirement increasing in the art is for gas-barrier (transmission-resistant) resin articles capable of preventing the contents from leaking out and protecting them from the open air for ensuring the safety and the storage stability of the contents and for protecting the environment from pollution. For those, polyamide resins are especially preferred and are used for various moldings, as their gas barrier properties are good. When wetted, polyamide resins become tougher, but, on the contrary, their dimensional stability and stiffness lowers. Especially when used in high humidity, their transmission resistance against liquid chemicals and gases lowers. Therefore, their use is often limited, and it is desired to improve them.
For improving for the physical properties of such polyamide resins, resin compositions and moldings consisting of a combination of polyamide resin and polyphenylene sulfide resin (hereinafter referred to as PPS resin) have heretofore been proposed, in which the PPS resin has good waterproofness and good transmission resistance but its toughness and moldability is not so good.
The method could improve the dimensional stability and the stiffness of the resin compositions and moldings in moisture over that of moldings of polyamide resin alone, but is till unsatisfactory. When the resin compositions and moldings are used for structures that are required to have good transmission resistance and toughness, they are not satisfactory. Therefore desired are molding materials that comprise polyamide resin and PPS resin and have both the good properties of polyamide resin and the good properties of PPS resin in good balance.
In multi-layer structures having a barrier layer of good barrier resin, one typical example of the resin to form the barrier layer is polyamide resin (for example, as in JP-A 220738/1983). However, the recent tendency in the field of automobile fuel is being toward using a mixture of gasoline and alcohol, gasohol, for which the plastic containers obtainable in the above-mentioned prior art are unsatisfactory in point of their barrier properties. Therefore desired is a technique of further improving the barrier properties of plastic containers.
On the other hand, it is known that PPS resin has extremely good barrier properties against liquid chemicals such as gasoline and automobile oil, and against water and carbon dioxide. Blow-molded containers and tubular structures of such PPS resin have been proposed (for example, as in JP-A 90216/1987, 255832/1986, 32816/1991). However, since its interlayer adhesiveness to other resin is poor, PPS resin has some problems in that its coextrusion and lamination with other resin materials such as polyethylene, polypropylene and other polyolefins is difficult.
The present invention is to realize a high-level balance of the mechanical strength and the toughness of polyamide resin and the low water absorption and the transmission resistance of PPS resin, and its object is to provide thermoplastic resin structures which are no improved to the highest possible degree that they are free from the reduction in the mechanical properties such as dimensional stability and stiffness and the reduction in the liquid chemical and vapor transmission resistance intrinsic to polyamide resin in moisture, especially to provide polyamide-PPS resin moldings favorable for vapor and/or liquid barrier articles, and to provide multi-layer structures of good transmission resistance, moldability, workability, interlayer adhesiveness and toughness that are favorable to plastic containers and can be stably and economically formed into good plastic containers.